A common type of vehicular powertrain includes a transmission with a torque converter and a gearbox. Traditionally, the gearbox remains engaged when the vehicle comes to a stop in Drive mode, such as when stopping for a traffic light. In this condition, the transmission continues to exert some load on the engine and to transmit some torque, called creep torque, to the vehicle wheels. When the driver releases the brake pedal but doesn't immediately depress the accelerator pedal, this creep torque keeps the vehicle from rolling backwards even on moderate uphill grades.
The load on the engine increases fuel consumption while the vehicle is idling in drive. One approach to reduce fuel consumption while the vehicle is stationary is to automatically release a transmission clutch to put the gearbox into a neutral state. The clutch is automatically re-engaged when the brake pedal is released. This reduces the load on the engine during idle, but also eliminates the creep torque during the interval between brake pedal release and re-engagement of the clutch. If the vehicle is stopped on an uphill grade, the vehicle may roll backwards at first, which is disconcerting to the driver.